Existing sensors rely on phenomena that do not support high sensitivity, remote monitoring of parameters such as magnetic fields and the like. For example, Hall Effect sensors detect the voltage generated by the drift of charge carriers when a magnetic field is applied to a current. Other sensors rely on detecting the Lorentz force of a magnetic field on a current carrying wire. Still others such as magnetostriction layer sensors incorporate the lengthening effect on ferromagnetic materials such as cobalt and Terfenol-D® magnetostrictive alloy when exposed to magnetic fields. Terfenol-D® is a registered trademark of Edge Technologies, Inc.
Magnetoresistive element sensors or ordinary magnetoresistive sensors commonly incorporate flux concentrators and measure the decrease in resistance as a function of applied magnetic field. Other sensors incorporate effects such as giant magneto-impedance (GMI). GMI, employs, for example, a NiFe coated BeCu wire. High frequency current is passed through the wire and the resistance component of its impedance is measured. This resistance measurement reflects the presence of magnetic fields. These sensors can be very temperature dependent, resulting in either poor accuracy or expensive correction measures. Such sensors therefore have disadvantages regarding size, price, power, and data output access.
Other physical parameters are readily measured in the current art. Temperature is typically measured through the voltage caused by the Seebeck effect of a thermocouple, by the resistance change of a resistance-temperature device (RTD), or by the change in current-voltage properties of a semiconductor diode junction.
Electric fields are measured through direct measurement of potential between two conductive probes (voltmeter) of known spacing and through non-linear effects (second order effects) on devices through modulation of an elastic constant (electro acoustics) or conduction band bending (semiconductors).
The AWD based measurements offer a universal method to the measurement of a physical parameter as it affects an electrical lumped element, the element then allowing a number of physical structures and interactions with a physical measurand.
What is needed, therefore, are techniques for sensing that provide for very small size, low price, low-power operating range, passive, wireless, and contactless method of measurement and remote interrogation.